In punching machines where the tools are carried on rotating magazines, it is a general desire that tool changing can be done as quickly as possible. In the original simple turret press, this can be easily achieved by rotating the turret magazine so that the tool is directly moved into the working position. This operation can be carried out with the help of numerical control without difficulty. In this way very rapid automatic tool changing can be achieved with changing times of only two or three seconds.
In further types of punching machines, the tools are carried on separate rotating magazines and transferred from the magazine to special guides in the working position with the help of tool changers. The turret magazine can then be placed at a distance from the point of operation of the tool, the tool changer gripping the tool in the magazine and transferring it to the guides in the operational position. Such tool changers are also automated these days and can be program-controlled. Such a tool changer is shown in U.S. Pat. No. 3,765,291. In this case the tool magazine is placed to one side of the machine frame, and the tools are moved a comparatively long distance from the magazine to the operation position where the tool is guided in a special fixed guide in combination with a complementary guiding portion formed by the gripping means of the tool changer.
The already known turret press offers certain advantages by its compact construction with rotatable turret magazines arranged in the immediate vicinity of the operation position of the tools. The turret magazine can suitably be placed in the gap of the machine frame, whereby a desired simple and compact construction is achieved. The conventional turret press has, however, certain disadvantages which are tied up with the fact that the tools are directly guided in the turret magazine. In a modern numerically controlled turret press it can be desirable to have as many as forty different tools in the magazine. This does not mean, however, that one can place any tool at all in an optional position in the magazine. A usual maximum diameter of a tool is 100 mm. If tools of this size were to be provided for in every position, the magazine would be unreasonably large and heavy. The tool positions in the upper magazine also serve, as already mentioned, as guides for the punch holders which are inserted in the magazine from its upper side. The diameter of the guide must therefore be at least as large as the diameter of the tool, and with forty tool positions this would give a pitch diameter of about 1.5 meter.
For this reason one is compelled to limit the number of tool positions for large diameters, and adjust the number of tools of different diameters in the magazine so that its diameter will not be unreasonably great. Such apparatus thus carries with it the disadvantage that only a limited number of tools having a larger diameter can be included in the magazine.
Further disadvantages in known turret presses with the tools guided in turret plates (turret magazines) have to do with the fact that tools with large diameter often have unsatisfactory guides, the wear occurring making necessary the costly exchange of the whole revolver plate.